That's the sound of steam bursting from the Earth at Nevada Geothermal's Blue Mountain project. Harnessing the earth's heat to generate electricity has long been an overlooked renewable resource, despite having produced power reliably in Italy since 1904.

You see, the Earth's heat never stops—meaning a geothermal power plant can produce electricity as regularly as a nuclear power plant can. And it also has nearly no emissions of the greenhouse gases causing climate change.

The U.S. produces more than 100,000 gigawatt-hours per year of geothermal electricity already, but it could produce as much as 3.2 trillion gigawatt-hours. So why isn't there more? Well, it comes down to economics. Unlike drilling to reach oil and natural gas fields, drilling for geothermal power doesn’t produce immediate dividends.

The U.S. Department of Energy aims to help with that by funding research into subsurface exploration. And right now near Reno, Nevada, U.S. government scientists and partners are testing an advanced geothermal technology that could make it available across the country. Here's hoping they make steam.

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